Shedding light on the MRI-driven dynamo in a stratified shearing box

• DOI: 10.1093/mnras/stae1011
• Publication Date: 2024-04-16T00:40:08Z
• Authors: Prasun Dhang; Abhijit B Bendre; Kandaswamy Subram...
• Keywords: Magnetic diffusivity; Induction equation; Magnetorotational instability; Solar dynamo

ABSTRACT We study the magneto-rotational instability (MRI) dynamo in a geometrically thin disc (H/R ≪ 1) using stratified zero net (vertical) flux shearing box simulations. find that mean fields and electromotive forces (EMFs) oscillate with primary frequency fdyn = 0.017 Ω (approximately nine orbital period), but also have higher harmonics at 3fdyn. Correspondingly, current helicity has two frequencies 2fdyn 4fdyn, which appear to be beat of EMFs, respectively, as expected from magnetic density evolution equation. Further, we adopt novel inversion algorithm called ‘Iterative Removal Of Sources’, extract turbulent coefficients mean-field closure EMFs obtained simulation. show an α-effect (αyy) is predominantly responsible for creation poloidal field toroidal field, while shear generates back indicating α–Ω-type operative MRI-driven accretion discs. both strong outflow ($\bar{v}_z$) pumping (γz) transport away mid-plane. Instead diffusivity, they are principal sink terms energy encouraging evidence generative effective α-effect. Finally, point out potential limitations horizontal (x − y) averaging defining ‘mean’ on extraction their physical interpretations.